Effects of varying Notch1 signal strength on embryogenesis and vasculogenesis in compound mutant heterozygotes

Abstract

Identifying developmental processes regulated by Notch1 can be addressed in part by characterizing mice with graded levels of Notch1 signaling strength. Here we examine development in embryos expressing various combinations of Notch1 mutant alleles. Mice homozygous for the hypomorphic Notch1 12f allele, which removes the single O-fucose glycan in epidermal growth factor-like repeat 12 (EGF12) of the Notch1 ligand binding domain (lbd), exhibit reduced growth after weaning and defective T cell development. Mice homozygous for the inactive Notch1 lbd allele express Notch1 missing an ~20 kDa internal segment including the canonical Notch1 ligand binding domain, and die at embryonic day ~E9.5. The embryonic and vascular phenotypes of compound heterozygous Notch1 12f/lbd embryos were compared with Notch1 +/12f , Notch1 12f/12f , and Notch1 lbd/lbd embryos. Embryonic stem (ES) cells derived from these embryos were also examined in Notch signaling assays. While Notch1 signaling was stronger in Notch1 12f/lbd compound heterozygotes compared to Notch1 lbd/lbd embryos and ES cells, Notch1 signaling was even stronger in embryos carrying Notch1 12f and a null Notch1 allele.